Vincent Sisson & Julia ??

Vincent Sisson was b 1778 in Fairfax Co, VA d 1850 in Jefferson Co, KY parents were Robert Sisson & Jane Powell.I need to find out what Julia's last name (if that was her name) and when he married her.They had 6 children:Ann, Atwell, James Lewis, Susan, Nancy, and unknown female (need her name, too.)